OBJECTIVE: To determine whether patent foramen ovale (PFO) is a risk factor for a cryptogenic cerebrovascular ischemic event (CIE). METHODS: This case-control study of 1072 residents of Olmsted County, Minnesota, who underwent contrast transesophageal echocardiography between 1993 and 1997 included 519 controls without CIE randomly selected from the population, 262 controls without CIE referred for transesophageal echocardiography because of cardiac disease, 153 cases with incident CIE of obvious cause (noncryptogenic), and 133 cases with incident CIE of uncertain cause (cryptogenic). RESULTS: Large PFOs were detected in 103 randomly selected controls (20.8%), 22 referred controls (8.4%), 17 noncryptogenic CIE cases (10.8%), and 22 cryptogenic CIE cases (16.5%). After adjustment for age, sex, hypertension, smoking, atrial fibrillation, ischemic heart disease, and number of contrast injections, the presence of a large PFO was not significantly associated with group status (P=.07). Using the odds of the presence of large PFO in the randomly selected controls as the reference, the odds ratio (95% confidence interval) of the presence of large PFO was 0.47 (0.26-0.87) for referred controls, 0.69 (0.37-1.29) for noncryptogenic CIE cases, and 1.10 (0.63-1.90) for cryptogenic CIE cases. CONCLUSIONS: Patent foramen ovale is not a risk factor for cryptogenic ischemic stroke or transient ischemic attack in the general population. The PFO's importance in the genesis of cryptogenic CIE may have been overestimated in previous studies because of selective referral of cases and underascertainment of PFO among comparison groups of patients referred for echocardiography for clinical indications other than cryptogenic CIE.
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